diff --git a/example/piano/main.go b/example/piano/main.go
index 89117d5d7..9868b1b11 100644
--- a/example/piano/main.go
+++ b/example/piano/main.go
@@ -103,6 +103,36 @@ func updateInput() {
 	}
 }
 
+var pianoImage *ebiten.Image
+
+func init() {
+	var err error
+	pianoImage, err = ebiten.NewImage(screenWidth, screenHeight, ebiten.FilterNearest)
+	if err != nil {
+		panic(err)
+	}
+	whiteKeys := []string{"A", "S", "D", "F", "G", "H", "J", "K", "L"}
+	width := 24
+	y := 48
+	for i, k := range whiteKeys {
+		x := i*width + 36
+		height := 112
+		pianoImage.DrawFilledRect(x, y, width-1, height, color.White)
+		common.ArcadeFont.DrawText(pianoImage, k, x+8, y+height-16, 1, color.Black)
+	}
+
+	blackKeys := []string{"Q", "W", "", "R", "T", "", "U", "I", "O"}
+	for i, k := range blackKeys {
+		if k == "" {
+			continue
+		}
+		x := i*width + 24
+		height := 64
+		pianoImage.DrawFilledRect(x, y, width-1, height, color.Black)
+		common.ArcadeFont.DrawText(pianoImage, k, x+8, y+height-16, 1, color.White)
+	}
+}
+
 func update(screen *ebiten.Image) error {
 	updateInput()
 	for i, key := range keys {
@@ -113,27 +143,7 @@ func update(screen *ebiten.Image) error {
 	}
 
 	screen.Fill(color.RGBA{0x80, 0x80, 0xc0, 0xff})
-
-	whiteKeys := []string{"A", "S", "D", "F", "G", "H", "J", "K", "L"}
-	width := 24
-	y := 48
-	for i, k := range whiteKeys {
-		x := i*width + 36
-		height := 112
-		screen.DrawFilledRect(x, y, width-1, height, color.White)
-		common.ArcadeFont.DrawText(screen, k, x+8, y+height-16, 1, color.Black)
-	}
-
-	blackKeys := []string{"Q", "W", "", "R", "T", "", "U", "I", "O"}
-	for i, k := range blackKeys {
-		if k == "" {
-			continue
-		}
-		x := i*width + 24
-		height := 64
-		screen.DrawFilledRect(x, y, width-1, height, color.Black)
-		common.ArcadeFont.DrawText(screen, k, x+8, y+height-16, 1, color.White)
-	}
+	screen.DrawImage(pianoImage, nil)
 
 	ebitenutil.DebugPrint(screen, fmt.Sprintf("FPS: %0.2f", ebiten.CurrentFPS()))
 	return nil
diff --git a/exp/audio/internal/audio.go b/exp/audio/internal/audio.go
index 0cff16ecf..1942493d2 100644
--- a/exp/audio/internal/audio.go
+++ b/exp/audio/internal/audio.go
@@ -18,8 +18,6 @@ var audioEnabled = false
 
 const SampleRate = 44100
 
-var currentPosition = 0
-
 type channel struct {
 	l                     []int16
 	r                     []int16
@@ -143,10 +141,8 @@ func loadChannelBuffer(channel int, bufferSize int) (l, r []int16) {
 
 		ch := channels[channel]
 		length := min(len(ch.l), bufferSize)
-		inputL := make([]int16, length)
-		inputR := make([]int16, length)
-		copy(inputL, ch.l[:length])
-		copy(inputR, ch.r[:length])
+		inputL := ch.l[:length]
+		inputR := ch.r[:length]
 		ch.l = ch.l[length:]
 		ch.r = ch.r[length:]
 		ch.nextInsertionPosition -= min(bufferSize, ch.nextInsertionPosition)
diff --git a/exp/audio/internal/audio_js.go b/exp/audio/internal/audio_js.go
index 4e7fdbd16..7be097c66 100644
--- a/exp/audio/internal/audio_js.go
+++ b/exp/audio/internal/audio_js.go
@@ -33,28 +33,21 @@ var (
 
 const bufferSize = 1024
 
-func audioProcess(channel int) func(e js.Object) {
-	return func(e js.Object) {
-		// Can't use 'go' here. Probably it may cause race conditions.
-		defer func() {
-			currentPosition += bufferSize
-		}()
+type audioProcessor struct {
+	channel int
+}
 
-		b := e.Get("outputBuffer")
-		l := b.Call("getChannelData", 0)
-		r := b.Call("getChannelData", 1)
-		inputL, inputR := loadChannelBuffer(channel, bufferSize)
-		const max = 1 << 15
-		for i := 0; i < bufferSize; i++ {
-			// TODO: Use copyToChannel?
-			if len(inputL) <= i {
-				l.SetIndex(i, 0)
-				r.SetIndex(i, 0)
-				continue
-			}
-			l.SetIndex(i, float64(inputL[i])/max)
-			r.SetIndex(i, float64(inputR[i])/max)
-		}
+func (a *audioProcessor) Process(e js.Object) {
+	// Can't use 'go' here. Probably it may cause race conditions.
+	b := e.Get("outputBuffer")
+	l := b.Call("getChannelData", 0)
+	r := b.Call("getChannelData", 1)
+	inputL, inputR := loadChannelBuffer(a.channel, bufferSize)
+	const max = 1 << 15
+	for i := 0; i < len(inputL); i++ {
+		// TODO: Use copyToChannel?
+		l.SetIndex(i, float64(inputL[i])/max)
+		r.SetIndex(i, float64(inputR[i])/max)
 	}
 }
 
@@ -69,7 +62,8 @@ func initialize() {
 	// https://developer.mozilla.org/ja/docs/Web/API/ScriptProcessorNode
 	for i := 0; i < MaxChannel; i++ {
 		node := context.Call("createScriptProcessor", bufferSize, 0, 2)
-		node.Call("addEventListener", "audioprocess", audioProcess(i))
+		processor := &audioProcessor{i}
+		node.Call("addEventListener", "audioprocess", processor.Process)
 		nodes = append(nodes, node)
 
 		dummy := context.Call("createBufferSource")
diff --git a/internal/graphics/framebuffer.go b/internal/graphics/framebuffer.go
index e08066d62..f1de5fb3a 100644
--- a/internal/graphics/framebuffer.go
+++ b/internal/graphics/framebuffer.go
@@ -53,10 +53,11 @@ func orthoProjectionMatrix(left, right, bottom, top int) *[4][4]float64 {
 }
 
 type Framebuffer struct {
-	native opengl.Framebuffer
-	width  int
-	height int
-	flipY  bool
+	native    opengl.Framebuffer
+	width     int
+	height    int
+	flipY     bool
+	proMatrix *[4][4]float64
 }
 
 func NewZeroFramebuffer(c *opengl.Context, width, height int) (*Framebuffer, error) {
@@ -100,6 +101,9 @@ func (f *Framebuffer) setAsViewport(c *opengl.Context) error {
 }
 
 func (f *Framebuffer) projectionMatrix() *[4][4]float64 {
+	if f.proMatrix != nil {
+		return f.proMatrix
+	}
 	width := NextPowerOf2Int(f.width)
 	height := NextPowerOf2Int(f.height)
 	m := orthoProjectionMatrix(0, width, 0, height)
@@ -107,7 +111,8 @@ func (f *Framebuffer) projectionMatrix() *[4][4]float64 {
 		m[1][1] *= -1
 		m[1][3] += float64(f.height) / float64(NextPowerOf2Int(f.height)) * 2
 	}
-	return m
+	f.proMatrix = m
+	return f.proMatrix
 }
 
 func (f *Framebuffer) Fill(c *opengl.Context, clr color.Color) error {